Method for repairing a turbine engine vane segment

ABSTRACT

A method for repairing a turbine engine vane segment of at least one airfoil disposed between band or platform members originally assembled in a designed relationship uses locating features integral with at least the band members and used in original assembly. For repair, the members are separated and at least one member is selected for reassembly, while preserving substantially in original form locating features of the selected member. A replacement member is provided for reassembly with the selected member, and the members are reassembled using the preserved locating features for positioning the members in the designed relationship. The apparatus provides elements for moving the segment members into and holding in the designed relationship.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is related to application No. 08/759,544 Rasch et al,for "Improved Turbine Engine Vane Segment," and to U.S. Pat. No.5,732,468 Galley et al, for "Method for Bonding a Turbine Engine VaneSegment," both filed concurrently with this application.

BACKGROUND OF THE INVENTION

This invention relates to the repair of components of turbine engines,for example repair of a vane segment of a turbine engine. Moreparticularly, it relates to the repair of a gas turbine engine turbinevane segment which has experienced high temperature operation in theengine.

During operation in the hot section of a gas turbine engine, portions ofair cooled vane segments which have been assembled into a vane assembly,sometimes called a nozzle or nozzle assembly, can become damaged to thepoint at which replacement or repair is required to maintain safe,efficient engine operation. Because such air cooled components arecomplex in design, are made of relatively expensive materials, and areexpensive to manufacture, repair is the desired choice. The capabilityfor repeating the repair, if necessary after subsequent operation, is ahighly desirable goal for any such repair method.

Various repair methods and apparatus have been widely reported and usedfor many years in the gas turbine engine art. One example is U.S. Pat.No. 4,305,697--Cohen et al., patented Dec. 15, 1981, relating to therepair of a gas turbine engine air cooled vane segment. One example of agas turbine nozzle showing, among other things, the axial, radial, andcircumferential positioning of the nozzle and its members in respect tothe engine is described in U.S. Pat. No. 5,343,694--Toborg et al.,patented Sep. 6, 1994. Identified in such patents are typical vaneassemblies to which this invention also relates. The disclosure of eachof such patents hereby is incorporated herein by reference.

During repair of such a vane segment, one or more of the components ofthe segment are removed and replaced. Frequently, at least the airfoilis replaced because of its exposure to strenuous airflow and hightemperature operating conditions. Replacement of an entire member of thesegment, such as one or more entire airfoils, requires preciserelocation of the replacement part in respect to other members of thesegment to provide between the members the relationship originallydesigned to enable proper airflow through the vane segment. Thatrelationship between the members of a vane segment is referred to hereinas the designed relationship.

In addition to the problem of precise relocation of the members whichcomprise the vane segment is the requirement to regenerate, such as bymachining, certain important vane segment features which are filled,covered or distorted during repair. Typical of such features are sealslots at circumferential borders of segment platforms. Known repairmethods typically fill such seal slots with brazing alloy or otheradditional material during repair, requiring remachining of such slotsafter reassembly of the repaired segment.

BRIEF SUMMARY OF THE INVENTION

The present invention, in one form, provides a method for repairing aturbine engine vane segment which comprises at least one airfoil membercarried between spaced apart first and second band members, sometimescalled platforms, which include cooperating first and second airfoilshaped openings, respectively, in each of the first and second bandmembers. The first and second band members and the airfoil member arepositioned axially, radially and circumferentially in respect to theturbine engine and relative to each other in a designed relationship.Each band member includes a plurality of locating features integral withthe band member and designed for use in positioning and aligning aplurality of vane segments with each other in the assembly of a turbineengine vane assembly.

The method comprises the steps of separating the airfoil member and theband members to provide separated segment members while preserving aplurality of the locating features, for example seal slots which arepreserved substantially in their original form, unfilled with additionalmaterial such as brazing alloy. Selected for reassembly is at least oneseparated segment member. At least one replacement member is providedfor reassembly with the selected segment member or members, an airfoilreplacement member having a first end shaped to cooperate with the firstairfoil shaped opening in the first band member and a second end shapedto cooperate with the second airfoil shaped opening in the second bandmember, a band replacement member having a replacement first or secondairfoil shaped opening and a plurality of locating features.

The selected separated and replacement members are assembled by holdingthe first and second band members in a spaced apart relationship by atleast a part of the preserved locating features; disposing the airfoilmember so that the ends are at the respective cooperating airfoil shapedopenings; moving the band members and the airfoil member by means of thelocating features into the designed relationship; and, while holding inthe designed relationship, securing the ends of the airfoil member atthe cooperating respective airfoil shaped openings.

In another form, the present invention provides apparatus for holdingthe band members at locating features and moving the band members intothe designed relationship with the airfoil disposed at the airfoilshaped openings. Such apparatus comprises a base, a band holder pedestalfixable to and projecting from the base, and a plurality of slide guidemembers, along with axial and circumferential clamping means. Thepedestal includes a plurality of distinct protrusions, for example pins,projecting substantially axially from the pedestal, and spaced apart andpositioned generally circumferentially at a distance from each othersubstantially the same as locating features in the base in the form ofcooperating band indentations, for example bolt holes, in at least oneof the band members. The axial clamping means is included to hold a bandmember axially in registry with the protrusions within the cooperatingband indentations. The plurality of slide guide members are spaced apartand movably carried on the base circumferentially, each slide guidemember carrying a plurality of generally radially disposed slides eachof which include a slide nose, for example a knife edge or an array of aplurality of aligned protrusions or pins, the slide noses being spacedapart at a substantially radial distance matching a designedrelationship radial distance between locating features in the bandmembers in the form of generally axially extending recesses, for exampleseal slots, each slide edge shaped to cooperate and be aligned with arecess in a band member. The circumferential clamping means is includedto hold each slide nose in a cooperating recess circumferentially.

In still another form, the present invention provides a method forassembling members of a vane segment including mounting and clamping avane segment preform in registry with the protrusions of the pedestal tohold the preform in the axial direction Then each slide guide member ismoved circumferentially toward the preform until the slide noses are inregistry with the cooperating recesses in each band member and clampedin that position by the circumferential clamping means. The preform isthereby positioned axially, radially and circumferentially.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded, perspective view of a gas turbine engine vanesegment including an inner platform, an outer platform and a pair of aircooled airfoils therebetween.

FIG. 2 is a diagrammatic plan view of the apparatus of the presentinvention for holding the vane segment in the designed relationship.

FIG. 3 is a perspective partially fragmentary view of the pedestal ofthe apparatus of FIG. 2 in position to receive an aft flange of thesegment.

FIG. 4 is a fragmentary view of the pedestal and aft flange of FIG. 3 inregistry, to enable holding such elements together.

FIG. 5 is a diagrammatic, perspective fragmentary view of a plurality ofparticularly spaced apart slides having noses in the form of knife edgescarried by a slide guide member of the apparatus of FIG. 2 movabletoward spaced apart recesses in the form of seal slots of the platformson one side of the vane segment

FIG. 6 is a fragmentary sectional view of the slides of FIG. 5 inposition within the seal slots.

DETAILED DESCRIPTION OF THE INVENTION

Generally, complex members of a vane segment, such as the hollow airfoilor the bands, sometimes called platforms, are precision cast because oftheir complexity and to develop desired mechanical properties andmicrostructure. Typically, a plurality of vane segments, each commonlyincluding an inner platform, an outer platform, and a plurality ofairfoils carried therebetween, as in the above incorporated Cohen et al.and Toborg et al. patents, are assembled circumferentially in respect toan engine axis to provide a vane or nozzle assembly. In order tofacilitate such assembly, certain features including surfaces,protrusions, indentations, openings such as holes, and recesses such asseal slots, are included in the original design of the member either inthe casting, in subsequent machining of the casting, or both. In thisdescription such features, identified in and discussed in connectionwith the attached drawings, are referred to as locating features for usewith the present invention.

FIG. 1 of the drawing is an exploded, perspective view of a gas turbinevane segment shown generally at 10 and including, as segment members, anouter platform or band shown generally at 12, an inner platform or bandshown generally at 14, and a pair of airfoils 16 between the spacedapart platforms. Outer platform 12 includes a pair of airfoil shapedfirst openings 18 shaped to cooperate with airfoil first ends 20,respectively as shown. Inner platform 14 includes a pair of airfoilshaped second openings 22 shaped to cooperate with airfoil second ends24, respectively as shown.

A plurality of the above discussed locating features on the inner andouter platforms can include, but are not limited to, recesses in theform of opposing seal slots 26A and 26C in the outer platform, and 26Band 26D in the inner platform. In addition, on the inner platform 14they can include opposing matefaces 28, other surfaces, such as aftsurface 31 of inner platform flange 30, surfaces of forward flange 35,and inner flange bolt holes 36. On outer platform 12, such locatingfeatures can include surfaces of aft flange 32, such as aft surface 29,and surfaces of forward lip 34, such as forward surface 37. A pluralityof such locating features exist on the segment members from originalmanufacture and are preserved substantially in their original form, andused for holding and repositioning selected separated segment andreplacement members in the designed relationship, according to a form ofthe present invention.

When a vane segment is evaluated for repair, frequently one or moresegment members can be repaired by patching, brazing, welding, orotherwise adding material and then refinishing to provide a refurbished,serviceable component without separating individual members of thesegment However, there are a number of instances in which one or moremembers of a segment, typically an airfoil, are damaged to the point atwhich such relatively less complicated repair is not practical and thedamaged member must be replaced in the segment assembly. It has been apractice in the gas turbine repair art to separate members of thesegment, replace a damaged member and reassemble members of the segment.Such separation of members can be accomplished in a variety of ways. Oneis to remove the airfoils from the platforms by mechanically cutting offthe airfoils from the platforms and regenerating airfoil shaped openingsin the platforms by such material removal methods as electrodischargemachining. Another method of separation involving heating and thenpulling to separate members at a brazed joint is described in U.S. Pat.No. 5,444,911--Goodwater, et al., patented Aug. 29, 1995, the disclosureof which hereby is incorporated herein by reference.

According to the present invention, whatever is the method of separationof members of a segment, a plurality of the above described type oflocating features originally included in the platforms for initialmanufacture are preserved substantially in their original form. As wasmentioned above, known repair methods have included filing, changing,obscuring or covering, rather than preserving in substantially originalform, such locating features, particularly recesses such as seal slots,which then later, after repair, must be regenerated such as bymachining. Such preserved locating features, according to the presentinvention, are used in the repair method of the present invention toreposition members into the designed relationship during reassembly.Preservation of such locating features for such use reduces oreliminates costly procedures needed for regenerating such features whichare essential to the function of the assembly. In addition, use of theoriginal, preserved locating features to accurately position and holdsegment members in the form of a segment preform prior to finishingrequires only a very small amount of initial securing by welding, suchas minimal tack welding which does not affect or distort members of thesegment. At the same time, such use minimizes the amount of repairmaterial, such as braze alloy, needed to be added to the segment preformto regenerate required dimensions of the finished segment.

Certain known repair practices employ extensive welding, typically gastungsten arc welding, to secure members of a segment and to add materialto regenerate required dimensions. Although such welding and alloys usedfor welding can develop mechanical properties greater than do brazingtype alloys, such extensive welding has resulted in distortion anddamage to a segment being repaired. Frequently, brazing alloys then areapplied to correct such defects, frequently filling recesses such asseal slots, and requiring additional machining of the brazed portion torestore segment dimensions. As can be appreciated from all of suchoperations to correct defects resulting from welding distortion, suchknown repair processes can be costly to conduct. In addition, whilealloys such as brazing alloys or mixtures have sufficient mechanicalproperties to cover many such defects, none achieve the level ofmechanical properties of the original material of the member. Over time,repeated and extensive application of these relatively weaker materials,as has been certain prior practice in the art, results in reducingsubsequent repairability of the segment. Practice of the presentinvention, including preserving and using locating features to relocateaccurately members of a segment, greatly reduces requirements for repairwelding as well as the amount of braze repair material added to thesegment. In this way, use of the invention significantly increases thetotal life of the segment. During evaluation of the present invention, anozzle segment of a gas turbine high pressure turbine nozzle, as shownin FIG. 1 and having members made of the commercially known andavailable X-40 cobalt base alloy, was observed to include damagedairfoils which needed to be replaced. Members of the nozzle segment wereseparated to provide the outer platform 12, the inner platform 14, andthe two airfoils 16. Such separation was accomplished by mechanicallycutting off the two airfoils adjacent the platforms and discarding thedamaged airfoils. Selected for reassembly with two replacement airfoilswere the separated outer and inner platforms. Material from the originalairfoils 16 in the airfoil shaped slots 18 of the inner and outerplatforms was removed and slightly larger airfoil shaped slots tofacilitate reassembly were regenerated by commercial electrodischargemachining using appropriately shaped electrodes. The selected platformswere positioned in spaced apart relationship, for example in theapparatus of the present invention, which held the platforms atpreserved locating features in the designed relationship. Then themembers were secured in that position.

In this example, the members were positioned and held using theapparatus of the present invention shown in FIGS. 2, 3, 4, 5 and 6 ofthe drawings. FIG. 2 is a diagrammatic plan view of such apparatusincluding a base 38 to which is fixed a pedestal 40 projecting from thebase. Projecting axially, using engine related directions shown byarrows in the drawings, from pedestal 40 are a plurality of distinctprotrusions, for example pins 42, aligned and spaced apart generallycircumferentially substantially the same as cooperating locatingfeatures in a platform member, for example indentations in the form ofbolt holes 36 in inner platform 14. Such spacing is represented bydistance D in the partially fragmentary perspective view of FIG. 3.Associated with pedestal 40 is axial clamping means represented by forcearrows 44 in the drawings, for example in the form of one or more "L"shaped members which is releasably attached to pedestal 40, such as byscrews, and is shaped to press platform 14 toward pedestal 40. Theapparatus also includes a plurality of slide guides 46, shown in moredetail in the perspective view of FIG. 5 and the fragmentary sectionalview of FIG. 6. The slide guides are spaced apart generally in thecircumferential direction and are carried by the base. The slide guidescan be fixed to base 38 or can be movable thereon generally in thecircumferential direction, for example in slide grooves 48. Each slideguide carries a plurality of generally radially disposed slides 50,shown in more detail in FIGS. 5 and 6, for example in the form ofknife-like edges or noses 52. Although the noses are shown assubstantially continuous surfaces or edges, it should be understood thatsuch noses are intended to include a series or array of pins or otherprotrusions which together perform the function of a nose or edge. Slidenoses 52 are spaced apart at a generally radial distance, such asdistance H in FIG. 5, which matches a radial distance betweencooperating preserved locating features in the inner and outer band orplatform members, for example the axially extending recesses in the formof seal slots 26A and 26B in the platforms, as shown in FIG. 5. Eachslide nose is shaped to cooperate and register in alignment with suchrecess. In this example, the slides were held in the slide guides byfriction, although a common type of clamping means can be used.

During practice of the method using the apparatus of the presentinvention in one form shown in the drawings, a segment preform isprovided by relatively loosely assembling a pair of replacement airfoils20 in their respective airfoil shaped openings 18 and 22 in theseparated and selected outer and inner platforms 12 and 14,respectively. The replacement airfoils were relatively loosely coldfitted into the slightly larger airfoil shaped openings. This preformthen was positioned, as shown in FIG. 3, so that the bolt holes 36 ofinner platform 14 were aligned with pins 42 projecting from pedestal 40.The platform was then moved toward pedestal 40 until pins 42 were inregistry with, for example abutting or disposed within, bolt holes 36 asshown in FIG. 4. Axial clamping means 44 was engaged to hold pins 42within bolt holes 36, thereby holding the preform in the axialdirection.

With the inner platform secured in this position, a pair of slides 50were moved circumferentially toward the preform through channels 56 inslide guides 46. Each slide 50 included a nose in the form of aknife-like edge 52, spaced apart radially at a distance H generallymatching a designed relationship radial distance between preserved sealslots 26A and 26B on one side of the platform, and preserved seal slots26C and 26D on the other side of the platform. In this example of theembodiment shown in FIGS. 5 and 6, slide guides 46 were fixed to base 38and slides 50 were movable through channels 56, as shown by arrows 58 toprovide flexibility to the operation of the slide guides. The slideswere moved circumferentially toward cooperating, opposed seal slotsuntil the slide noses were in registry with respective seal slots,thereby positioning the inner and outer platforms, with the airfoilstherebetween, in the designed relationship. The fragmentary sectionalview of FIG. 6 shows noses 52 of slides 50 held by friction 54 inregistry with their respective cooperating preserved seal slots 26A and26B. In this example, in order to more accurately position thereplacement airfoils 16 within their respective airfoil shaped openingsin which they were releasably held, alloy shims were placed in junctures60, identified in FIG. 5.

With the members of the segment preform restrained in the apparatus inthe designed relationship, separate, discrete gas tungsten arc tackwelds were spaced about the juncture 60 between the replacement airfoilsand the inner and outer platforms to secure the position of the membersin the designed relationship. Typically, only about 3 or 4 tack weldsabout each juncture were applied for such purpose. No distortion of anyof the members resulted from such tack welding. Then a brazing alloypowder mixture, of the type described in U.S. Pat. No.4,830,934--Ferrigno, et al. (patented May 16, 1989), was applied to suchjuncture of the segment preform which was then heated to the alloybrazing temperature. The disclosure of that patent hereby isincorporated herein by reference. Dimensional inspection of the nozzlesegment assembly generated in this example showed that the matefaces,lips, flanges, seal slots and flange holes were within acceptabledimensional values and did not have to be refinished. Only one flangemachined surface required some build up. Practice of the presentinvention has been shown to be a more simple, economical and efficientmethod for the repair of turbine engine vane segments.

The present invention has been described in various forms in connectionwith specific examples, embodiments and combinations. However, it willbe understood by those skilled in the arts involved that this inventionis capable of a variety of modifications, variations and amplificationswithout departing from its scope as defined by the appended claims.

We claim:
 1. In a method for repairing a turbine engine vane segmentcomprising at least one airfoil member carried between spaced apartfirst and second band members which include cooperating first and secondairfoil shaped openings, respectively, in each of the first and secondband members, the first and second band members and the airfoil memberbeing positioned axially, radially and circumferentially in respect to agas turbine engine and to each other in a designed relationship, eachband member including a plurality of locating features integral with theband member and designed for use in positioning and aligning a pluralityof vane segments in respect to each other in assembly of a turbineengine vane assembly, the steps of:separating the airfoil member and theband members to provide separated segment members while preserving aplurality of the locating features as preserved locating features;selecting for reassembly at least one separated segment member;providing for reassembly with the selected separated segment member atleast one replacement member selected from the group consisting of: a)an airfoil replacement member having a first end shaped to cooperatewith the first airfoil shaped opening in the first band member and asecond end shaped to cooperate with the second airfoil shaped opening inthe second band member, and b) a band replacement member having areplacement first or second airfoil shaped opening and a plurality oflocating features; and, assembling the selected separated and thereplacement members by: a) holding the first and second band members ina spaced apart relationship by at least a part of the preserved locatingfeatures with the airfoil member disposed between the band members sothat the first end is at the first airfoil shaped opening and the secondend is at the second airfoil shaped opening, b) moving the band membersand the airfoil member, by means of the locating features, into thedesigned relationship, and c) while holding in the designedrelationship, securing, respectively, the first and second ends of theairfoil member to the first and second band members at the first andsecond airfoil shaped openings.
 2. The method of claim 1 in which thepreserved locating features include in each band member generallycircumferentially extending opposing seal slots which are preservedsubstantially unfilled with additional material.
 3. The method of claim2 in which the preserved locating features include, in addition, atleast one generally axially extending hole in at least one band member.4. The method of claim 1 in which the ends of the airfoil member and theband members are secured by:first tack welding the ends of the airfoiland their respective band member intermittently about a juncturetherebetween at the airfoil shaped openings; and then, brazing the endsto the band members at the juncture.
 5. The method of claim 1 inwhich:the vane segment is a segment of a gas turbine engine turbinenozzle including a plurality of airfoil members; and, the bands are vaneplatforms.
 6. The method of claim 1 for replacing an airfoil member of aturbine engine vane segment, comprising the steps of:selecting forreassembly the first and second band members; separating the airfoilmember and the first and second band members to provide cooperatingfirst and second airfoil shaped openings, respectively, in each of thefirst and second band members while preserving locating featuresincluding generally circumferentially extending generally radiallyspaced apart opposing seal slots in each band member and at least onegenerally axially extending hole in at least one of the band members;providing a replacement airfoil member; and, assembling the replacementairfoil and the selected band members into a segment preform with thefirst and second ends of the airfoil disposed at their respectivecooperating airfoil shaped openings in the selected band members;holding at least one band member of the preform axially at the preservedaxially extending hole; holding the band members generallycircumferentially at the preserved seal slots and radially spaced apartat a distance which positions the airfoil member and the band members inthe designed relationship axially, radially and circumferentially; andthen, securing the first and second airfoil end and the first and secondband members into a repaired turbine engine vane segment.